1. Field of the Invention
The invention generally relates to an apparatus for interrupting a light beam in response to the application of a predetermined force and more particularly to an optical switch for use, for example, in fiber optic control circuits as well as fiber optic data transmission lines.
2. Description of the Prior Art
Traditionally, control circuits utilize electrical switches to control relays and other electromechanical devices. These devices are coarse control elements and may be utilized because they are relatively insensitive to contact bounce as well as noise pick-up on associated wiring. Generally, this type of control circuit is too slow for many modern, fast-response systems and subject to failure due to wear, pitting and burning of the electrical contacts.
It is desirable to interface electrical switches with electronic circuits such as microprocessors and to perform power control functions utilizing solid-state relays. Such solid-state electronics eliminate some of the above problems but are still susceptible to contact bounce and noise pick-up problems. Contact bounce can be countered with added anti-bounce circuitry and filtering. Both solutions tend to reduce response speed as well as increase the cost, weight, complexity and size of the overall system.
The noise pick-up problem is of particular concern in many military applications where digital computers are required to operate in the presence of severe electromagnetic pulses. Further, all onboard flight computers in commercial aircraft must be capable of operating in the presence of electrical storms. In industrial applications, computers are required to operate in many noisy environments, as, for example, electrical noise generated by spot welding as well as the opening and closing of electromagnetic relays. The computer can be protected from stray electrical noise by heavily filtering input power lines and adequate shielding of the electronics. However, if a remote keyboard is used to provide input to the computer, the wiring between keyboard and computer can allow stray electrical noise to be picked up in the computer thereby negating the effectiveness of the shielding.
One solution to the problem is to convert the electrical output of a shielded conventional keyboard into an optical output which can be transmitted to the computer by means of fiber optic transmission lines. The fiber optic transmission lines perform the same function as electrical transmission lines; however, they offer distinct advantages since the fiber optic dielectric materials are immune to noise pick-up problems.
An alternative solution to the problem involves utilizing a local keyboard composed of an array of optical switches which directly interface with a computer through fiber optic transmission lines. This solution eliminates the need for electronics within the keyboard, electrical power to the keyboard as well as shielding of the keyboard.